We are analyzing the interactions between virus glycoproteins and their receptors for several enveloped viruses important for human health. Our goals are to define mechanisms of virus fusion and entry, elucidate mechanisms of virus tropism, identify cellular receptors, develop strategies to elicit and detect neutralizing antibodies, and develop novel therapeutic and preventative approaches. 1) Human herpesvirus 6 (HHV-6) is the etiologic agent of exanthema subitum and causes opportunistic infections in immunocompromised patients; it has also been implicated in multiple sclerosis and in the progression of AIDS. We previously identified human CD46 as the major receptor for the two major HHV-6 subgroups (A and B). During the past year, we determined that HHV-6 uses domains 2 and 3 of CD46; this differs from measles virus, which uses domains 1 and 2. We also identified gH as the HHV-6 glycoprotein involved in binding to CD46. 2) Human herpesvirus 8 (HHV-8) is associated with Kaposi?s sarcoma, a major opportunistic disease associated with HIV infection. During the past year, we established a specific fusion assay between cells chronically infected with HHV-8 (and presumably expressing the surface glycoproteins) and various target cells. HeLa and RK13 cells proved to be particularly effective targets, whereas NIH 3T3 cells were relatively ineffective. We have also expressed several of the individual HHV-8 recombinant glycoproteins, and have begun to raise rabbit antisera against specific peptides. This work hopefully will set the stage for identification of the HHV-8 receptor. 3) Hepatitis C virus is a major human pathogen associated with chronic liver disease and hepatocellular carcinoma. Research on this virus is severely hampered by the absence of a suitable cell culture system in which to propagate the virus and study its life cycle. We have expressed molecular chimeric variants of both the E1 and E2 glycoproteins that enable surface expression of these glycoproteins. The E1/E2 expressing cells were shown to fuse with hepatocyte cell lines in a low pH-induced manner. We are optimizing this system for analysis of neutralizing antibodies, and for screening cDNA libraries for the cellular receptor(s). In addition, we have begun developing a system employing HCV subviral particles to study entry of this virus.